Ring contractions of 4-oxoquinolizine-3-diazonium tetrafluoroborates, by an aza Wolff rearrangement, to alkyl indolizine-3-carboxylates

The 1-substituted 3-amino-4H-quinolizin-4-ones 13, available in two steps f rom 10 and methyl (Z)-2-benzyloxycarbonylamino-3-(dimethylamino)prop enoate (11), were diazotized to give the stable diazonium tetrafluoroborates 7a a nd 7b. Heating of these diazonium salts in alcohols gave mixtures of 3-unsu bstituted quinolizine derivatives 8a and 8b and the alkyl indolizine-3-carb oxylates 9a-h. The ratio of the two types of products 8 and 9 was dependent on the type of alcohol employed. Thus, treatment of 7a or 7b with 2-propan ol predominantly resulted in the 3-unsubstituted quinolizinones 8, while tr eatment of 7a or 7b with primary alcohols gave the indolizine-3-carboxylate s 9 as the major products in most cases. The transformation of the 4-oxoqui nolizine-3-diazonium tetrafluoroborates 7a and 7b into the alkyl indolizine -3-carboxylates 9a-h represents the first example of a Wolff rearrangement in the fused cyclic alpha -diazoamide series.